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Originally Posted by Bill Haywood
1. Is the acceleration of the expansion of the universe due to dark energy overcoming gravity? Dark energy pushes space apart, and as matter gets spread out, the gravitational force pulling it together lessens, so dark energy romps?
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Basically yes. As the universe keeps expanding, dark energy will dominate more and more. In the future, far away galaxies that we can see now will be practically invisible since they will be so red shifted. And it's for the reasons you said....as the matter density goes down gravity becomes weaker but dark energy stays constant.
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2. Red shift and photons. Some time ago, someone on this board told me that photons themselves have higher and lower energy, or something. The photon that's part of a blue wave will be different from one in a red wave. Ok, so how do we make this consistent with the Doppler effect? Simply by changing perspective from in front to behind a moving object, the wavelength changes, but that would mean that the hotness of the photons themselves would also be relative. Wot.
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Right...the energy of a photon is observer dependent so if you start moving really fast toward/away from the sun you would observe the photons to be higher or lower energy than what you observe them to be now.
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